1. Field of the Invention
The present invention relates to a technology for relaying calls on a line where a communication path is established through a cell transmission network by call setting control every time communications are needed.
2. Description of the Related Art
Lately, along with the spread of in-house LANs, etc., a WAN (Wide Area Network) node apparatus for integrating and accommodating conventional telephone audio traffic, low-speed data lines and LAN traffic, and dynamically securing relay bands for LAN traffic with a high burst characteristic, has been demanded.
For a technology for dynamically utilizing a relay band, an ATM (Asynchronous Transfer Mode) multiplex technology for transmitting each set of data after logically multiplexing a plurality of fixed length cells of data, has been examined mainly in a broad band field, and now this ATM multiplex technology has also come to be applied to a narrow band field.
In this case, for trunk lines, existing STM (Synchronous Transfer Mode) dedicated lines are used in which a multiplex access service is available, and a hybrid multiplex technology for transmitting ATM cells to be communicated between nodes using a predetermined one of or a plurality of time division channels of the STM dedicated line is being developed. By adopting such a configuration, an ATM multiplex technology capable of flexibly corresponding to traffic fluctuations and suitable for highly efficient transmissions, and a TDM (Time Division Multiplex) technology capable of guaranteeing transmission line quality, can be united.
In such a technological background, today an ATM-WAN node apparatus capable of terminating ATM dedicated lines or STM dedicated lines in which a multiplex access service is available, is being increasingly demanded.
Accordingly, a technology for relaying calls (SVC call: Switched Virtual Circuit call) on in-house lines where a communication path is established every time communications are needed using an ATM network comprised of ATM dedicated lines or STM dedicated lines as one function of such an ATM-WAN node (AWN) apparatus, such as an extension telephone network or ISDN (Integrated Services Digital Network), etc., becomes necessary.
For conventional technologies, in the case of relaying SVC calls on an ATM network, a technology called xe2x80x9cnetwork interworkxe2x80x9d and a technology called xe2x80x9cservice interworkxe2x80x9d are well known.
FIG. 1 shows the connection form of a path in a conventional network interwork system.
An ATM-WAN node 102 at site A (corresponding to a branch office) and an ATM-WAN node 102 at site B, are connected by an ATM trunk line 104 comprised of ATM dedicated lines or STM dedicated lines. At each site a Private Branch Exchange (PBX) 101A accommodating N-ISDN (Narrow band Integrated services digital network) lines controlled by a common channel signalling system or a Private Branch Exchange (PBX) 101B accommodating audio channels controlled by a channel associated signalling system, are accommodated in an interwork function unit (IWF) 103 in the ATM-WAN node 102.
In a network interwork system, a path setting operation between the ATM-WAN nodes 102 varies depending on whether the signalling system of the line is a common channel signalling system or a channel associated signalling system.
First, when the signalling system of the line is a common channel signalling system, two kinds of ATM communication paths; an ATM communication path (D channel ATM-VCC) for relaying call setting N-ISDN signals (D channel signals), in which a call setting message specified by an N-ISDN common channel signalling system is stored, and an ATM communication path (B channel ATM-VCC) for communicating data (audio signals), are secured every time a communication request is issued from a terminal device (telephone set, etc.) connected to a PBX 101A at one site to a terminal device (telephone set, etc.) connected to a PBX 101A at the other site. Then, the call setting N-ISDN signal processed by the PBX 101A is transparently transmitted in the D channel ATM-VCC.
On the other hand, when the signalling system of the line is a channel associated signalling system, only one kind of ATM communication path is secured between the ATM-WAN nodes 102 at each site every time a communication request is issued from a terminal device (telephone set, etc.) connected to the PBX 101A at one site to a terminal device (telephone set, etc.) connected to the PBX 101A at the other site. Then, both of the call setting channel associated signals in which the call setting message specified by a channel associated signalling system and the data (audio signals), are transmitted on the ATM communication path.
However, in the conventional network interwork system shown in FIG. 1, since the transfer methods of call setting messages between the ATM-WAN nodes 102 in the case where the signalling system of the line is a common channel signalling system and in the case where the system is a channel associated signalling system, are different from each other, there is a problem that communication cannot be performed between PBXs 102 accommodating lines of different signalling systems.
FIG. 2 shows the connection form of a path in a conventional service interwork system.
In a service interwork system, when a communication request is issued from a terminal device (telephone set, etc.) connected to a PBX 101A at one site to a terminal device (telephone set, etc.) connected to a PBX 101A at the other site, the IWF 103 of the ATM-WAN node 102 on a calling party side converts a call setting message in each call setting signal to a call setting message of a B-ISDN (Broad band Integrated Services Digital Network) format, regardless of whether a call setting N-ISDN signal is transmitted from a PBX 101A or whether a call setting channel associated signal is transmitted from a PBX 101B.
Then, the above-mentioned IWF 103 transmits a call setting B-ISDN signal in which a call setting message is in the above-mentioned B-ISDN format, to the IWF 103 of the ATM-WAN node 102 on a called party side using a specific ATM call setting path on an ATM trunk line 104.
After extracting a call setting message in a B-ISDN format from the call setting B-ISDN signal, the IWF 103 of the ATM-WAN node 102 on the called party side converts the message to a call setting N-ISDN signal or a call setting channel associated signal, and transfers the signal to the PBX 101A or PBX 101B.
However, in the conventional service interwork system shown in FIG. 2, in the information elements of the call setting message set in the call setting N-ISDN signal of a common channel signalling system, there is an element which cannot be set by the call setting B-ISDN signal. Accordingly, the conventional service interwork system has a problem that there are some services which cannot be provided in the services supported by an N-ISDN signal.
FIG. 3 and FIG. 4 show the data format of a SET-UP message in a B-ISDN format and the data format of a SET-UP message in an N-ISDN format, respectively.
Although in a SET-UP message in both the B-ISDN and N-ISDN formats, a plurality of information elements are transmitted following a protocol identifier, call reference and message class, for example, a display information element, key pad facility information element, signal information element, feature activation information element, feature indication information element, etc. transmitted in a SET-UP message in an N-ISDN format as shown in FIG. 4, cannot be transmitted in a SET-UP message of a B-ISDN format as shown in FIG. 3.
The present invention was made in the above-mentioned background, and it is an object of the present invention to enable communications, even between PBXs accommodating lines of different signalling systems, and to enable the relay of information elements of a call setting message in all the signalling systems.
The present invention comprises a cell transmission apparatus (ATM-WAN node 502) for relaying calls on a line (SVC line) where a communication path is established by call setting control every time communications are needed, through a cell transmission network (ATM network).
First, a transmitting side signalling format editing repeater device (IWF 503, etc.) edits the signalling format of call setting signals corresponding to each call from a line (PBX 501) into a common channel format, and relays the call setting signals edited into a common channel format as cell data (ATM cell) using a common call setting signal transmission path (ATM call setting path, and a connection for N-ISDN call setting). Alternatively, the transmitting side signaling format editing repeater device edits the signalling format of call setting signals from a line, into a channel associated format, adds path identification information for identifying a user signal transmission path to the call setting signals edited into a channel associated format, and sends the signal to a common call setting signal transmission path as cell data. Alternatively, a signalling format decision table (signalling system decision table) for registering the signalling formats of call setting signals for each cell transmission device on the called party side is provided, whereby the transmitting side signalling format editing repeater device edits the signalling format of call setting signals corresponding to each call from a line into a signalling format determined by referring to the signalling format decision table, and sends the signals on a common call setting signal transmission path as cell data.
Then, the receiving side signalling format editing repeater device (IWF 503) edits the call setting signals edited into a common channel format which is received from the common call setting signal transmission path as cell data into a signalling format corresponding to the signalling format of call setting signals of the called party side line, and transfers the signals to the called party side line. Alternatively, the receiving side signalling format editing repeater device edits the call setting signals edited into a channel associated format which is received from the common call setting signal transmission path into a signalling format corresponding to the signalling format of the call setting signals of the called party side line identified by path identification information which is added to the call setting signals, and transfers the edited call setting signals to the called party side line. Alternatively, the receiving side signalling format editing repeater device edits the call setting signals edited into a common channel or channel associated format which are received from the common call setting signal transmission path as cell data, into a signalling format corresponding to the signalling format of the call setting signals of the called party side line identified by path identification information which is added to the call setting signals, and transfers the edited call setting signals to the called party side line.
Then, a user signal repeater device (CLAD 1102, etc.) relays as cell data user signals communicated in the call using a user signal transmission path (ATM communication path, and a connection for audio communications) established corresponding to the call for each call communicated on the line.
At this time, in the above-mentioned signalling format decision table, signalling formats corresponding to each of the lines are registered for each calling party side line. Alternatively, in the signalling format decision table, signalling formats corresponding to each of the lines for each called party side line are registered.
According to the above-mentioned configuration of the present invention, line signals can be accommodated in a cell transmission network such as an ATM network, etc. while the line service level of a variety of signalling systems such as a common channel signalling, channel associated signalling, etc., are guaranteed.
Furthermore, even between lines of different signalling systems, WAN communications relayed through a cell transmission network such as an ATM network, etc. become available.